Printed circuit board edge connector

ABSTRACT

A printed circuit board assembly and method of assembly is provided for a printed circuit board having a top and bottom surface with at least one edge portion having a rounded surface extending from the top surface to a point below the top surface and at least one electrical contact pad located on the top surface and extending over the edge portion rounded surface to a point below the top surface.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to printed circuit board connectors. Inparticular, the present invention relates to printed circuit board edgeconnectors.

2. Description of the Related Art

Printed circuit (PC) cards or printed circuit boards (PCBs) havetraditionally provided mechanical support for electronic componentswhile providing electrical interconnections of these components. Onemeans to connect a printed circuit board to other electronic circuitryis to provide a printed circuit board edge connection assembly using aseries of contact pads fabricated and arranged in a row at the edge ofthe printed circuit board. These edge contact pads are electricallyconnected to the components upon the printed circuit board. Further, toconnect the circuitry on a printed circuit board to other electronicsystem components, a printed circuit board socket connector is providedthat receives a printed circuit board and its edge contact pads. Thisprinted circuit board socket contains several metal contact springspositioned in the socket such that the insertion of the printed circuitboard into the socket results in individual metal contact springsresting upon the surface of the printed circuit board and, specifically,contacting an individual one of the edge contact pads.

A typical prior art printed circuit board edge connection assembly isshown in part in FIG. 1A. In FIG. 1A, four contact spring connectors104, 106, 108, and 110 are arranged to be placed upon four printedcircuit board edge contact pads 112, 114, 116, and 118 which are uponthe top surface 120 of the printed circuit board 100. Since the fourcontact spring connectors 104, 106, 108, and 110 are part of a printedcircuit board edge connection socket (not shown) the contact springconnectors 104, 106, 108, and 110 are positioned when the printedcircuit board 100 is inserted into the socket so that the contact springconnectors 104, 106, 108, and 110 rest on top of the printed circuitboard edge contact pads 112, 114, 116, and 118 to form an electricalconnection.

The contact spring connectors 104, 106, 108, and 110 and the printedcircuit board edge contact pads 112, 114, 116, and 118 are typicallyplated with gold over nickel to minimize contact surface corrosion. Oneof the main problems with the contact edge connector assembly shown isthe excessive wear of the contact spring connector bottom surface whenmating the printed circuit board to the printed circuit card edgeconnector socket (not shown) containing the contact spring connector.Referring to FIG. 1B, a cross section view of FIG. 1A, as the printedcircuit board 100 is inserted into the socket (not shown), the contactspring connector 110 first contacts the printed circuit board front edge102 and, as the insertion continues, rides over the top of this edge 102and then contacts the front edge of the printed circuit edge contact pad118 upon the printed circuit board surface 120. Typically, the printedcircuit board edge 102 of printed circuit board 100 is formed with arouter bit resulting in a sharp edge having exposed glass fibers fromthe glassy epoxy laminate material of the printed circuit board.Continuing the insertion, the contact spring connector 110 rides overthe edge of the contact pad 118 and onto the surface of the contact pad118. During this insertion, the contact spring connector 110 hastraveled over the printed circuit board edge 102 and then the contactpad 118 edge which can result in wearing of the contact spring connectorsurface plating. Many printed circuit board insertions will remove thegold and nickel plating leaving the contact spring connectorssusceptible to corrosion which may cause reliability problems. Inaddition, other problems with the printed circuit board edge connectionassembly of FIGS. 1A and 1B include the amount of force required to matethe printed circuit board with the printed circuit board socket,stubbing that may result in damage to the spring connector andmisalignment of the spring connector during insertion that may result inshorting between across adjacent contact pads.

Alternate solutions to these problems are shown in FIGS. 2, 3, 4 and 5.In FIG. 2, a cross section view, a printed circuit board 200 includes afront edge 202 having chamfer edges 206 and 208. The chamfer edges 206may reduce the edge scraping wear of a contact spring connector 210 asit engages the printed circuit board 200 and comes to rest upon the topof the contact pad 218. However this arrangement still results inwearing of the bottom surface of the contact spring connector 210 withlittle to no effect on the insertion force required.

FIG. 3 is another embodiment shown in cross section illustrating aprinted circuit board 300 having a TEFLON (a trademark of DuPont) edge302 which provides an inclined surface 306 to receive the contact springconnector 310 to reduce the printed circuit board edge connectioninsertion force and reduce wear on the spring contact connector 310.However, the addition of the Teflon cap 302 increases the complexity ofthe printed circuit board assembly resulting in an increase inmanufacturing cost.

A further embodiment shown in cross section in FIG. 4 illustrates aprinted circuit board 400 having a rounded front edge 402 with a surfacecoating of epoxy. Surface 406 is the first contact point for the contactspring connector 410 as the printed circuit board 400 is inserted. Theuse of the epoxy coating on the printed circuit board edge 402 reducesthe insertion force required to assemble the printed circuit board intothe printed circuit board edge connector socket and reduces wear on thecontact spring connectors. However, the step of adding the epoxy coatingexposes the contact pads, such as contact pad 418, to contamination andthis step also adds complexity to the printed circuit board assemblyresulting in increased manufacturing costs.

Another embodiment is illustrated in FIG. 5 which is a cross sectionview of a printed circuit board 500 including a continuous flex circuitfilm 504 completely covering a thermally conductive stiffener which istypically a metal plate. A contact pad 502 is fabricated on the surfaceof the flexible circuit film 504. As the printed circuit board 500 isinserted into a printed circuit board edge connector socket (not shown)a contact spring connector 510 will first encounter the flex circuitfilm before it contacts the edge contact pad 502 riding up on thecontact pad 502 edge indicated as 506. It should be understood for thisembodiment, the flexible circuit film covers the entire printed circuitboard. As such, only the flexible film surface is available for themounting of electrical components electronic components and wiring. Inother words, it is a two layer printed circuit board assembly. Howeverthe continuous flexible circuit film does reduce the insertion forcerequired to mat the printed circuit board with a printed circuit boardedge connector socket and reduces wear on the contact spring connectorsduring the insertion process. Providing a continuous flexible circuitfilm bonding onto a conductive stiffener increases the cost of theprinted circuit board manufacture and decreases the versatility of theprinted circuit board assembly since only two layers are available forall electronic component wiring.

SUMMARY

In accordance with the present invention, a printed circuit boardassembly is provided that include top and bottom surfaces and having atleast one edge portion with a rounded surface extending from the topsurface to a point below the top surface and at least one electricalcontact pad located on the top surface extending over the top surfaceonto the rounded surface of the edge portion to a point below the topsurface.

In addition, a method is provided for manufacturing a printed circuitboard including the steps of covering an edge portion of the printedcircuit board to form a rounded surface edge and fabricating contactpads upon the top of the printed circuit board which extend over therounded edge portion of the printed circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1A is an isometric view of an edge portion of a printed circuitboard assembly including several contact pads and corresponding contactspring connectors;

FIG. 1B is a cross section view of the printed circuit board assembly ofFIG. 1A;

FIG. 2 is a cross section view of an edge portion of a printed circuitboard assembly having chamfer edges;

FIG. 3 is a cross section view of an edge portion of a printed circuitboard assembly having a Teflon cap on the edge portion;

FIG. 4 is a cross section view of an edge portion of a printed circuitboard assembly having an epoxy coated edge;

FIG. 5 is a cross section view of an edge portion of a printed circuitboard assembly having a continuous flexible circuit film bonded about aconductive stiffener;

FIG. 6A is an isometric view of a first embodiment of the presentinvention including an edge portion of a printed circuit board assemblyhaving contact pads fabricated on a flexible circuit film coverextending over the edge of the printed circuit board assembly;

FIG. 6B is a cross section view of the printed circuit board assembly ofFIG. 6A;

FIG. 7A is an isometric view of a second embodiment of the inventionincluding an edge portion of a printed circuit board assembly with apartial flexible circuit film covering containing openings for contactpads fabricated upon the printed circuit board surface;

FIG. 7B is a cross section view of the printed circuit board assembly ofFIG. 7A;

FIG. 8A is an isometric view of a third embodiment of the inventionillustrating an edge portion of a printed circuit board assembly with aflexible circuit film covering containing openings sized for the contactpads fabricated upon the printed circuit board surface;

FIG. 8B is a cross section view of the printed circuit board assembly ofFIG. 8A;

FIG. 9A is an isometric view of a fourth embodiment of the inventionincluding an edge portion of a printed circuit board assembly includingtwo partial flexible circuit film coverings;

FIG. 9B is a cross section view of the printed circuit board assembly ofFIG. 9A;

FIG. 10A is a flowchart illustrating the manufacturing process for theprinted circuit board assembly of FIGS. 6A and 6B;

FIG. 10B is a flowchart illustrating the manufacturing process for theprinted circuit board assembly of FIGS. 7A and 7B;

FIG. 10C is a flowchart illustrating the manufacturing process for theprinted circuit board assembly of FIGS. 8A and 8B; and

FIG. 10D is a flowchart illustrating the manufacturing process for theprinted circuit board assembly of FIGS. 9A and 9B.

DETAILED DESCRIPTION

The following is intended to provide a detailed description of examplesof the invention and should not be taken to be limiting of the inventionitself. Rather, any number of variations may fall within the scope ofthe invention, which is defined in the claims following the description.

The present invention is a printed circuit board edge connector assemblythat reduces the insertion force required to insert a printed circuitboard into a printed circuit board edge connection socket assembly whilereducing wear upon contact surfaces of contact spring connectors withinthe printed circuit board edge connection socket. Also provided is amethod for producing the printed circuit board edge connector assembly.

In the figures only a single row of printed circuit board edge contactpads on top of a printed circuit board is shown. However, as typical formany printed circuit boards, contact pads can be formed on both the topand bottom surfaces of the printed circuit board and the top and bottomcontact pads mate respectively with top and bottom spring connectors ina printed circuit board edge connector socket.

FIG. 6A is an isometric view of an edge portion of a printed circuitboard 600 having a rounded edge that includes a flexible circuit film602 bonded thereupon. The flexible circuit film 602 covers only a frontedge portion of the printed circuit board 600. Therefore, the printedcircuit board portion surface 620 is exposed and includes printedcircuit board contacts such as 622 mounted upon the printed circuitboard surface 620 and which are interconnected to wiring and componentsof the printed circuit board (not shown). In other words, the printedcircuit board 600 is otherwise as typical multilayer circuit board thatcan include a number of wiring layers in excess of two. Fabricated onthe flexible circuit film 602 is a series of edge contact pads 612, 614,616, and 618. Each of these contact pads include a tab (shown forcontact pad 618 as tab 624) which extends over the printed circuit boardcontact 622 to be soldered to the printed circuit board contact 622enabling the contact pad 618 to be electrically connected to otherwiring traces within the printed circuit board 600 and any electricalcomponents mounted thereon. The contact pads 612, 614, 616 and 618 arefabricated upon the flexible circuit film 602 in a manner that extendsthe contact pad surface on the top surface of the printed circuit board620 over the edge portion such that the front part of the contact pad618 (shown as 626) is positioned below the top surface of the printedcircuit board 600. When the printed circuit board 600 is inserted into aprinted circuit board edge connection socket (not shown) containing aseries of contact spring connectors, shown as 604, 606, 608, and 610,the first point of contact of the contact spring connectors with theprinted circuit board 600 will be the contact pads.

This is illustrated in FIG. 6B (which is a cross section view of theassembly of FIG. 6A). In FIG. 6B, the contact spring connector 610 firstmakes contact with a front portion 626 of the contact pad 618. Sinceboth the contact spring connector 610 and the contact pad 618 are goldand nickel plated, any wear on the contact spring connector 610 surfacewill be minimized when the printed circuit board is inserted into theprinted circuit board edge connection socket.

FIG. 7A illustrates a second embodiment of the present invention. FIG.7A is an isometric view illustrating an edge portion of a printedcircuit board 700 containing contact pads 712, 714, 716 and 718fabricated on the surface of the printed circuit board 700. Thesecontact pads 712, 714, 716, and 718 may form electrical connections toother wiring layers within the printed circuit board 700 in atraditional manner. A flexible film 702 is sized and fabricated to covera front edge portion of the printed circuit board 700 such that the film702 includes openings exposing the contact pads 712, 714, 716 and 718.In reference to contact pad 718, the opening 732 in the film 702includes a front portion in front of the contact pad 718 that exposes arounded edge portion 730 of the printed circuit board 700. The opening732 also exposes the contact pad 718 so that when the printed circuitboard is inserted into a printed circuit board edge connection socket,the contact spring connectors 704, 706, 708 and 710 will first encounterthe rounded edge of the printed circuit board 700 and then ride onto thecontacts pads 712, 714, 716 and 718. The openings, such as 730 for thecontact spring connector 710, provides a guide channel for the contactspring connector 710 as it travels to rest upon the surface of thecontact pad 718. For example, a wall 734 formed by the flexible circuitfilm 702 prevents the contact spring connector 710 from laterallydeviating from the surface of the contact pad 718. This is also shown ina cross-sectional view in FIG. 7B illustrating how the contact springconnector 710 enters the opening 730 in front of the connection pad 718and, as the insertion continues, travels on top of the front edgeportion 740 of the contact 718 while being laterally restrained by theflexible circuit film wall 734.

FIG. 8A is a third embodiment of the invention similar to the embodimentshown in FIG. 7A. In FIG. 8A, four contact pads 812, 814, 816 and 818are fabricated on the surface of a printed circuit card 800. A flexiblefilm 802 partially covers the edge portion of the printed circuit card800 as shown. The flexible film 802 includes several openings whichexpose the edge contact pads 812, 814, 816, and 818 when the flexiblefilm 802 is bonded to the surface of the printed circuit board 800. Oneflexible film opening 830 is shown to expose edge contact pad 818. Fourcontact spring connectors 804, 806, 808 and 810 are shown to bepositioned such that when the printed circuit board 800 is inserted intoa printed circuit board edge connector socket (not shown) these contactspring connectors 804, 806, 808, and 810 do not make contact with thetop surface of the printed circuit board 800 but make first contact withthe flexible film 802 as they travel to rest upon the top of the edgecontact pads 812, 814, 816 and 818. This is shown in FIG. 8B which is across-sectional view of the assembly in FIG. 8A. Referring to FIG. 8B,the contact spring connector 810 first makes contact with the flexiblefilm 802 when the printed circuit card board 800 is being inserted inthe printed circuit board edge connector socket. The flexible film 802causes the contact spring connector 810 to rise above the printedcircuit board rounded edge and come to rest upon contact pad 818 as theprinted circuit board 800 is being inserted. Since the flexible film ismuch less abrasive than the printed circuit board surface, this assemblyminimizes wear of the contact spring connector 810 bottom surface.

A fourth embodiment of the present invention is illustrated in FIG. 9A.In this embodiment, a printed circuit board 900 includes a rounded edgeportion that is partially covered by a first flexible circuit film 902.Four edge contact pads 912, 914, 916, 918 are formed on top of thisflexible circuit film 902. These edge connector pads include a tab, suchas 924 for edge contact pad 918 that is soldered to a printed circuitboard contact 922 fabricated on the surface of printed circuit board900. This connection of the tab 924 to the contact 922 electricallyconnects the edge connector pad 918 to other wiring of the printedcircuit card 900. Edge contact pads 912, 914, 916, and 918 includeportions that extend over the edge of the current circuit board 900conforming to the rounded edge surface on top of the flexible circuitfilm 902. A second flexible film 920 is placed on top of the firstflexible circuit film 902. The second flexible film 920 includesopenings such a shown such as 924 shown for edge contact pad 918 whichexpose the edge contact pads while providing a guiding and channelingstructure including a wall 934. Contact spring connectors 904, 906, 908and 910 are positioned in FIG. 9A to electrically contact edge connectorcontact pads 912, 914, 916 and 918 respectively. A cross-section view ofthe assembly of FIG. 9A is shown in FIG. 9B. When the printed circuitboard 900 is inserted into a printed circuit board edge connector socket(not shown) the contact spring connector 910 will make first contactwith this printed circuit board assembly 900 (as shown in FIG. 9B) byfirst contacting the edge contact pad 918 through an opening 940 of thesecond flexible film 920. Additionally a wall 934 provided by the secondflexible film 920 will guide the contact spring connector 910 as theprinted circuit card 900 is inserted.

FIGS. 10A, 10B, 10C and 10D illustrate flowcharts for the manufacturingprocess for the printed circuit board assemblies of FIGS. 6A, 7A, 8A and9A respectively.

For manufacturing the printed circuit board connectors shown in FIGS. 6Aand 6B, FIG. 10A illustrates the process beginning with the fabricationof the printed circuit board in step 1001. The printed circuit boardedge portion is radiused or rounded in step 1002 which can be formedwith a router or equivalent shaping tool. For step 1003, the flexcircuit is typically fabricated using a 1 or 2 mil thick layer ofpolyimide or KAPTON material in a flat sheet form. In step 1004, thecopper circuitry is formed using typical photo lithographic techniquesstarting with a copper foil that is adhesively laminated or plated up onthe surface of the polyimide sheet. The photo lithographic processes areused to expose the resist and etch away the excess copper material toform the contact pads. The tab 624 that is cantilevered over the edge ofthe polyimide film requires processing techniques that are common withtape automated bonding technology. The section of the polyimide filmthat is located under the cantilevered tab 624 is removed and replacedwith a temporary filler material that can be selectively removed afterthe copper circuitry is patterned on the top surface of the polyimidefilm. The section of polyimide film can be removed using a mechanicalpunch and die or other techniques including laser or chemical etching.The temporary filler material is used to fill the section of thepolyimide film that was removed and provides a smooth surface for thecopper circuitry to be patterned. The filler material can be selectivelyremoved without damaging the copper circuitry that is patterned on thesurface of the polyimide sheet. After the copper circuitry pattern isformed on the polyimide film, the contact pads are plated with a layerof nickel and overplated with gold to provide a reliable contactinterface for the card edge connector.

Multiple sections of contact pads are typically formed on a singlepolyimide sheet. After the copper circuitry is formed and the contactpads have been plated, the sections of contact pads are cut to fit theedge of the circuit card and formed and adhesively bonded to the edge ofthe card. Special attention is required during the forming operation toprevent damage to the contact pads and to prevent delamination of curvedportion of the pads from the polyimide sheet. In step 1005, attention isalso required to ensure precise alignment of the cantilevered contacttab extensions with the solder pads 622 on the circuit card. Typicalsolder reflow assembly processes are used to form the solderedconnections between the cantilevered tabs on the flex circuit 624 andthe pads 622 on the circuit card.

FIG. 10B illustrates the process for fabricating the printed circuitboard edge connectors of FIGS. 7A and 7B. In step 1011, the printedcircuit board is fabricated followed by the step 1012 where the contactpads are formed upon the printed circuit board by typical photolithographic techniques and step 1013 connected to appropriate printedcircuit board conductive traces. The printed circuit board edge is thenrounded similar to step 1002 in FIG. 10A. In step 1015, the flex film isfabricated from the same polyimide sheet used in the flex circuitdescribed for FIGS. 6A and 6B. However, an increased thickness of thematerial is needed. The exact thickness of the material depends on thethickness of the contact pads on the circuit card. It is desirable forthe thickness of the flex film to be 2-3 mils thicker than the thicknessof the contact pads. The flex film fabrication techniques includecreating the openings in the sheet of polyimide and a sizing operationto cut the sections of flex film to fit the circuit card edge. Theopenings in the sheet of polyimide material can be formed by amechanical punch and die tool or using a laser or chemical etchingprocess. The sections of flex film are formed. In step 1016, the flexfilm is adhesively bonded to the edge of the circuit card. Specialattention is required to ensure precise alignment of the openings in theflex film with the contact pads on the circuit card edge. Specialattention is also required to prevent the adhesive on the flex film fromcontaminating the surface of the contact pads on the circuit card.

In FIG. 10C, the method of fabricating printed circuit board edgeconnectors FIG. 8A, and 8B include techniques that are the same in FIG.10B. In other words, steps 1021, 1022, 1023 and 1024 are the same assteps 1011, 1012, 1013, and 1014 respectively of FIG. 10B. However, forstep 1025, the thickness of the polyimide sheet is matched to thethickness of the contact pads on the circuit card. Also, the geometry ofthe openings in the flex film are made to match the geometry of thecontact pads on the circuit card. Lastly, step 1026 is the same as step1016 in FIG. 10B.

The fabrication techniques for this embodiment of FIGS. 9A and 9Bcombine the fabrication techniques for the flex circuit used in FIGS. 6Aand 6B along with fabrication techniques used for the flex film in FIGS.7A and 7B. Specifically for FIG. 10D, steps 1030, 1031, 1032, 1033, and1034 are the same as steps 1001, 1002, 1003, 1004, and 1005 respectivelyfor FIG. 10A. For steps 1035 and 1036, the second flex film, similar tothe one shown in FIGS. 7A and 7B, is formed and adhesively bonded to thesurface of the first flex circuit.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that,based upon the teachings herein, that changes and modifications may bemade without departing from this invention and its broader aspects.Therefore, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention. Furthermore, it is to be understood that theinvention is solely defined by the appended claims. It will beunderstood by those with skill in the art that if a specific number ofan introduced claim element is intended, such intent will be explicitlyrecited in the claim, and in the absence of such recitation no suchlimitation is present. For non-limiting example, as an aid tounderstanding, the following appended claims contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimelements. However, the use of such phrases should not be construed toimply that the introduction of a claim element by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim element to inventions containing only one such element,even when the same claim includes the introductory phrases “one or more”or “at least one” and indefinite articles such as “a” or “an”; the sameholds true for the use in the claims of definite articles.

The invention claimed is:
 1. A method of fabricating a printed circuitboard with an edge connector comprising the steps of: fabricating aprinted circuit board having at least one electrically conductive pathon a top surface of the printed circuit board, fabricating a roundededge of the printed circuit board, forming an edge connector contact padupon the top surface portion of the printed circuit board andelectrically connecting the contact pad to the at least one conductivepath, and forming a layer over a portion of the printed circuit boardtop surface and extending the layer over the rounded edge to a bottomsurface portion of the printed circuit board and providing an opening inthe layer to expose the edge connector contact pad and further includingthe step of providing the first layer opening in front of the contactpad to expose a portion of the rounded edge of the printed circuit boardlocated adjacent to the edge connector contact pad.
 2. A method offabricating a printed circuit board with an edge connector comprisingthe steps of: fabricating a printed circuit board having at least oneelectrically conductive path on a top surface of the printed circuitboard, the printed circuit board having a thickness and a thicknessmidpoint at one half of the thickness, fabricating a rounded edge of theprinted circuit board, forming a first layer film over a portion of atop surface portion of the printed circuit board and extending over therounded edge to a bottom surface portion of the printed circuit board,forming a first edge connector contact pad upon a top surface portion ofthe first layer and extending over the first layer covering the roundededge to a point below the top surface of the printed circuit board andending above the thickness midpoint, electrically connecting the firstedge connector contact pad to the at least one conductive path, forminga second layer film on top of the first film layer and with a firstopening exposing the first edge connector contact pad and forming afirst wall surrounding the first edge connector contact pad.
 3. A methodof fabricating a printed circuit board according to claim 2 furtherincluding the step of forming a second edge connector located inparallel adjacency to the first edge connector and wherein the step offorming the second layer film includes the step of forming a secondopening exposing the second edge connector and forming a second wallsurrounding the second edge connector.
 4. A method of fabricating aprinted circuit board according to claim 1 wherein the layer formed overthe portion of the printed circuit board top surface includes a flexiblepolyimide film.
 5. A method of fabricating a printed circuit boardaccording to claim 2 wherein the layer formed over the portion of theprinted circuit board top surface includes a flexible polyimide film.